Compounds with isocyanate groups and masked groups reactive in relation to isocyanates

ABSTRACT

Isocyanato compounds with capped, isocyanate-reactive groups are those of the formula I ##STR1## where R 1  and R 2  are hydrogen, C 1  -C 10  -alkyl, C 6  -C 10  -aryl or C 7  -C 10  -aralkyl or together form C 3  -C 10  -alkanediyl, 
     X and Y are --O--, --S-- or ##STR2##  where R 4  is hydrogen, C 1  -C 20  -alkyl which is uninterrupted or interrupted by oxygen atoms in ether function, or is C 6  -C 10  -aryl or C 7  -C 10  -aralkyl, 
     R 3  is C 1  -C 10  -alkanediyl which together with --X--CR 1  R 2  --Y-- forms a 4-7-membered ring, 
     in which either one hydrogen in R 3  or the radical R 4  in ##STR3##  is replaced by an allophanate group R Ia  ##STR4##  in which R 5  is a divalent aliphatic, alicyclic, araliphatic or aromatic C 2  -C 20  hydrocarbon unit, 
     R 6  is a single bond or a divalent aliphatic, alicyclic, araliphatic or aromatic C 1  -C 20  hydrocarbon unit or a mono- or poly(C 2  -C 4  -alkylene oxide) unit, and 
     R 7  is a carbamoyl radical ##STR5## or a biuret group R Ib  ##STR6##  in which one R 8  is hydrogen and the other is as defined for R 7  or a biuret group R Ic  ##STR7##  in which one R 9  is as defined for R 7  and the other is as defined for R 1   
     or a thioallophanate group R Id  ##STR8##

The invention relates to isocyanato compounds (compounds containingisocyanate groups) with capped, isocyanate-reactive groups, of thegeneral formula I ##STR9## where R¹ and R² are hydrogen, C₁ -C₁₀ -alkyl,C₆ -C₁₀ -aryl or C₇ -C₁₀ -aralkyl or together form C₃ -C₁₀ -alkanediyl,

X and Y are --O--, --S-- or ##STR10## where R⁴ is hydrogen, C₁ -C₂₀-alkyl which is uninterrupted or interrupted by oxygen atoms in etherfunction, or is C₆ -C₁₀ -aryl or C₇ -C₁₀ -aralkyl,

R³ is C₁ -C₁₀ -alkanediyl which together with --X--CR¹ R² --Y-- forms a4-7-membered ring,

in which either one hydrogen in R³ or the radical R⁴ in ##STR11## isreplaced by an allophanate group R^(Ia) ##STR12## in which R⁵ is adivalent aliphatic, alicyclic, araliphatic or aromatic C₂ -C₂₀hydrocarbon unit,

R⁶ is a single bond or a divalent aliphatic, alicyclic, araliphatic oraromatic C₁ -C₂₀ hydrocarbon unit or a mono- or poly(C₂ -C₄ -alkyleneoxide) unit, and

R⁷ is a carbamoyl radical ##STR13## or a biuret group R^(Ib) ##STR14##in which one R⁸ is hydrogen and the other is as defined for R⁷ or abiuret group R^(Ic) ##STR15## in which one R⁹ is as defined for R⁷ andthe other is as defined for R¹

or a thioallophanate group R^(Id) ##STR16##

The invention additionally relates to crosslinking polyurethane coatingcompositions comprising compounds of the formula I and to coatingmethods in which these crosslinking polyurethane coating compositionsare used.

Crosslinking polyurethane coating compositions are generally known, forexample in the form of 2-component materials (cf. Kunststoff Handbuch,Volume 7, Polyurethane, 2nd Edition, 1983, Carl Hanser Verlag Munich,Vienna, pp. 540-561). These two-component systems contain a polyol asbinder and a compound having two or more free isocyanate groups ascrosslinking component.

Since a high molecular weight network develops after the two componentsare mixed, they can only be mixed directly prior to application to theworkpiece to be coated. For the processer of such systems this meansthat the individual coating steps must follow on smoothly from oneanother in terms of time, since following the mixing of the components adefined quantity of coating material must be processed within a certaintime.

This complication in the processing of these systems is accepted by theprocesser, since the resulting coatings are markedly superior to thoseobtained from the generally known, noncrosslinking one-componentsystems, which can in principle be stored for as long as is desired.

This superiority relates in particular to service properties such as

lack of sensitivity to mechanical stresses such as tension, extension,impact or abrasion

resistance to moisture (for example in the form of steam) and dilutechemicals

resistance to environmental effects such as temperature fluctuations andUV radiation

high gloss of the coated surfaces.

In order for coating materials to be able to be applied without problemsby conventional techniques, for example by spray application to thesurface to be coated, they should be of limited viscosity. Consequently,coating materials based on two-component systems usually includesolvents. However, the solvent content of these materials causesproblems, since the coatings processer has to take technically complexmeasures in order to avoid the passage into the atmosphere of thesolvents released during application and drying of the coatingmaterials. Consequently, many attempts have been made to find a way outof this situation of conflicting aims and to provide two-componentsystems which are not only of low viscosity coupled with high solidscontent but which also have a high profile in terms of theabovementioned service properties.

EP-A-0 585 835 describes two-component systems where the isocyanatecomponent comprises trimerized diisocyanates containing isocyanurategroups, where some of the remaining isocyanate groups are reacted with amonohydric alcohol to form urethane groups.

Polyisocyanates containing isocyanurate groups and allophanate groups,and formed from a diisocyanate and a polyester monoalcohol, aredescribed in DE-A-O 15 155. These polyisocyanates can be used ashardeners in two-component polyurethane coatings.

Additionally, in order to reduce the viscosity of the two-componentsystems, reactive diluents have been developed. These compounds have asimilar effect on the viscosity of two-component systems to that of asolvent. Unlike solvents, however, during the drying or hardening of thetwo-component systems employed as coating material the reactive diluentsreact with the other binder components to form a high molecular weightnetwork.

The German Patent Application with the file reference P 19524046.4describes a reactive diluent which is a compound containing oneisocyanate, one urethane and one thiourethane or urea group and 2capped, isocyanate-reactive groups. However, these compounds containneither an allophanate group nor a biuret group.

Despite the fact that it has already been possible with the previouslyknown two-component systems to make some progress regarding thereduction in the solvent content, there continues to be a need forimprovement in this respect.

It is therefore an object of the present invention to providetwo-component systems, which couple high solids content with lowviscosity and can be processed to give coatings with a good profile ofproperties, and components for such systems. It was also an object toprovide crosslinking one-component systems, which couple high solidscontent with low viscosity, are stable on storage and can be processedto give coatings whose quality is at least equal to those obtained fromtwo-component systems, and components for these one-component systems.

We have found that these objects are achieved by the isocyanatocompounds (I) defined at the outset which contain capped,isocyanate-reactive groups, and by crosslinking one-component andtwo-component polyurethane coating compositions comprising thesecompounds (I).

Among the novel compounds of the formula I preference is given to thosein which:

R¹ and R² are in particular hydrogen or C₁ -C₆ -alkyl, especiallymethyl, ethyl or isopropyl. Among the C₃ -C₁₀ -alkanediyl groups whichR¹ and R² can form together, cyclopentyl and cyclohexyl are preferred.

Preferred radicals R⁴ in the group ##STR17## which can be X and/or Y,are C₁ -C₆ -alkyl, for example methyl, ethyl, n-propyl or n-butyl.

Particularly suitable groups R³ are C₂ -C₁₀ -alkanediyls which, togetherwith --X--CR¹ R² --Y--, form a 5- or 6-membered ring.

In the compounds of the formula I it is necessary for either a hydrogenof R³, or R⁴, to be substituted by an allophanate group R^(Ia), a biuretgroup R^(Ib), a biuret group R^(Ic) or a thioallophanate group R^(Id).The compounds of the formula I therefore carry a single group selectedfrom the range of groups R^(Ia), R^(Ib), R^(Ic) and R^(Id). The groupwhich can be R^(Ia), R^(Ib), R^(Ic) or R^(Id) is referred to below asR^(I).

Particular preference is given to dioxolanes of the formula I.1##STR18## dioxanes of the formula I.2 ##STR19## in which R^(a) ishydrogen or C₁ -C₁₀ -alkyl, or oxazolidine derivatives of the formulaI.3 ##STR20##

The units R⁵ which are part of R^(I) are preferably units derived fromcustomary diisocyanates (cf. Kunststoff Handbuch, Volume 7,Polyurethane, 2nd Edition, 1983, Carl Hanser Verlag Munich, Vienna,Chapter 2.2.1) by abstraction of the two isocyanate groups.

Examples of customary diisocyanates are aliphatic diisocyanates such astetramethylene diisocyanate, hexamethylenediisocyanate(1,6-diisocyanatohexane), octamethylene diisocyanate,decamethylene diisocyanate, dodecamethylene diisocyanate,tetradecamethylene diisocyanate, derivatives of lysine diisocyanate,tetramethylxylylene diisocyanate, trimethylhexane diisocyanate ortetramethylhexane diisocyanate, cycloaliphatic diisocyanates such as1,4-, 1,3- or 1,2-diisocyanatocyclohexane,4,4'-di(isocyanatocyclohexyl)methane,1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)cyclohexane-(isophoronediisocyanate) or 2,4- or 2,6-diisocyanato-1-methylcyclohexane, andaromatic diisocyanates, such as 2,4- or 2,6-tolylene diisocyanate,p-xylylene diisocyanate, 2,4'- or 4,4'-diisocyanatodiphenylmethane, 1,3-or 1,4-phenylene diisocyanate, 1-chloro-2,4-phenylene diisocyanate,1,5-naphthylene diisocyanate, diphenylene 4,4'-diisocyanate,4,4'-diisocyanato-3,3'-dimethylbiphenyl, 3-methyldiphenylmethane4,4'-diisocyanate, or diphenyl ether 4,4'-diisocyanate. Mixtures ofthese diisocyanates can also be present. Preference is given tohexamethylene diisocyanate and isophorone diisocyanate, and to 2,4- and2,6-tolylene diisocyanate and 2,4'- and 4,4'-diphenylmethanediisocyanate.

R⁶ preferably comprises branched and unbranched C₁ -C₄ -alkanediyl,especially methylene or ethylene. Other suitable units R⁶ are mono- orpoly(C₂ -C₄ -alkylene oxide) units of the formula ##STR21## in whichalkylene is branched or unbranched C₁ -C₄ -alkanediyl, n is 1-20 andR^(b) independently at each occurrence is methyl, ethyl or hydrogen.

In this context, both homopolymeric and copolymeric units derived fromethylene oxide, propylene oxide or butylene oxide are suitable.

The novel compounds of the formula I are employed as the B component intwo-component polyurethane coating compositions, commonly in the form ofmixtures (B) comprising

a) compounds of the general formula I,

b) customary isocyanates having on average at least 2 isocyanate groups(compounds II),

c) compounds of the formula III ##STR22## where R¹ and R² are as definedfor formula I,

U and V are --O--, --S-- or ##STR23## where R¹¹ is hydrogen, C₁ -C₁₀-alkyl which is uninterrupted or interrupted by oxygen atoms in etherfunction, or is C₆ -C₁₀ -aryl or C₇ -C₁₀ -aralkyl, and

R¹⁰ is C₁ -C₁₀ -alkanediyl which together with --U--CR¹ R² --V-- forms a4-7-membered ring, in which either one hdyrogen of R¹⁰ or the radicalR¹¹ in ##STR24## is substituted by a urethane group R^(IIIa) ##STR25##or a urea group R^(IIIb) ##STR26## or a urea group R^(IIIc) ##STR27## ora thiourethane group R^(IIId) ##STR28## in which R⁵ and R⁶ are asdefined for formula I.

Examples of suitable, customary isocyanates having on average at least 2isocyanate groups (compounds II) are triisocyanates such as2,4,6-triisocyanatotoluene, triphenylmethane triisocyanate or2,4,4'-triisocyanatodiphenyl ether, or the mixtures of di-, tri- andhigher polyisocyanates which are obtained by phosgenization ofcorresponding aniline/formaldehyde condensation products and constitutepolyphenyl polyisocyanates containing methylene bridges.

Compounds II of particular interest are customary polyfunctionalaliphatic polyisocyanates of the following groups:

(a) polyisocyanates which contain isocyanurate groups and are derivedfrom aliphatic, cycloaliphatic, aromatic and/or araliphaticdiisocyanates. Particularly preferred in this context are thecorresponding isocyanato-isocyanurates based on hexamethylenediisocyanate and isophorone diisocyanate. The present isocyanurates are,in particular, simple trisisocyanatoalkyl or trisisocyanatocycloalkylisocyanurates, which constitute cyclic trimers of the diisocyanates, orare mixtures with their higher homologs containing more than oneisocyanurate ring. The isocyanato-isocyanurates generally have an NCOcontent of from 10 to 30% by weight, in particular from 15 to 25% byweight, and a mean NCO functionality of from 2.6 to 4.5.

Particularly suitable compounds II are isocyanurates of the generalformula (IIa) ##STR29## or the oligomeric forms derived therefrom, inwhich R⁵ is as defined for the compounds of formula I.

(b) Diisocyanates containing uretdione groups and having isocyanategroups attached to aromatic, aliphatic and/or cycloaliphatic structures,preferably derived from hexamethylene diisocyanate or isophoronediisocyanate. In the case of polyuretdione diisocyanates, these aredimerization products of diisocyanates.

(c) Polyisocyanates containing biuret groups and having isocyanategroups attached to aliphatic structures, especiallytris(6-isocyanatohexyl)biuret or mixtures thereof with its higherhomologs. These polyisocyanates containing biuret groups generally havean NCO content of from 10 to 30% by weight, in particular from 18 to 25%by weight, and a mean NCO functionality of from 2.8 to 4.5.

(d) Polyisocyanates containing urethane groups and/or allophanate groupsand having isocyanate groups attached to aliphatic or cycloaliphaticstructures, as can be obtained, for example, by reacting excessquantities of hexamethylene diisocyanate or isophorone diisocyanate withpolyhydric alcohols such as trimethylolpropane, glycerol,1,2-dihydroxypropane or mixtures thereof. These polyisocyanatescontaining urethane groups and/or allophanate groups generally have anNCO content of from 12 to 25% by weight and a mean NCO functionality offrom 2.5 to 4.5.

(e) Polyisocyanates which contain oxadiazinetrione groups and arepreferably derived from hexamethylene diisocyanate or isophoronediisocyanate. Polyisocyanates of this kind, containing oxadiazinetrionegroups, can be prepared from diisocyanate and carbon dioxide.

(f) Carbodiimide- or uretonimine-modified polyisocyanates.

It is also possible for some of the isocyanate groups in theabovementioned polyisocyanates (a) to (f) to be reacted withmonoalcohols.

Particularly suitable compounds of the formula III are known, forexample, from the German Patent Application with the file reference P.195 24 046.4.

Preferred units R¹, R², R⁵ and R⁶ in the compounds of the formula IIIare the same as those for the corresponding units of the formula I. Ingeneral, units R¹⁰, R¹¹, U and V in formula III differ from thecorresponding units R³, R⁴, X and Y in formula I only in that they maycarry the group R^(IIIa) instead of the group R^(Ia), the group R^(IIIb)instead of the group R^(Ib), the group R^(IIIc) instead of the groupR^(Ic) and the group R^(IIId) instead of the group R^(Id).

The compounds of the formula I are prepared with particular simplicityby reacting compounds of the formula IV ##STR30## where R¹ and R² are asdefined for formula I,

D and E are --O--, S or ##STR31## where R¹³ is hydrogen, C₁ -C₁₀ -alkylwhich is uninterrupted or interrupted by oxygen atoms in ether function,or is C₆ -C₁₀ -aryl or C₇ -C₁₀ -aralkyl, and

R¹² is C₁ -C₁₀ -alkanediyl which together with D-CR¹ R² -E forms a4-7-membered ring,

in which either one hydrogen in R¹² or the radical R¹³ in ##STR32## issubstituted by a radical R^(IVa)

    --R.sup.6 --OH,

a radical R^(IVb)

    --R.sup.6 --NH.sub.2,

or a radical R^(IVc) ##STR33## or a radical R^(IVd)

    --R.sup.6 --SH

with a compound of the formula V

    OCN--R.sup.5 --NCO                                         V

at from 20 to 140° C. with a molar ratio of the compound of formula IVto the compound of formula V of from 1:1.5 to 1:20.

The reaction is generally performed without solvent or in solution andpreferably under atmospheric pressure.

By choosing the starting compound IV with the appropriate substituentsR^(IVa), R^(IVb), R^(IVc) or R^(IVd) it is possible to prepare specificnovel compounds of the formula I and compounds of the formula III. Theunits D, E and R¹² in the starting compounds (compounds IV) differ fromthe corresponding units U, V and R¹⁰ (compounds III) and X, Y and R³(compounds I) in the target compounds only, generally speaking, in thatthey carry different substituents R^(IVa), R^(IVb), R^(IVc) and R^(IVd)(compounds IV), R^(IIIa), R^(IIIb), R^(IIIc) and R^(IIId) (compoundsIII) and, respectively, R^(Ia), R^(Ib), R^(Ic) and R^(Id) (compounds I).The lower case letters a, b, c or d in the designations for the startingcompounds and target compounds and in their characteristic radicals areallocated such that they are equal in the starting compounds and in thetarget compounds which can be prepared therefrom (in other words, forexample, a compound with the substituent R^(IVa) leads to Ia, with R¹,R², R⁵ and R⁷ being identical in both the starting and the targetcompound). Owing to their ease of preparation, particular preference isgiven to mixtures of compounds I, II and, if appropriate, III which areformed in the reaction of the corresponding starting compounds IV and V.

The reaction is usually ended when the starting compound of the formulaIV in the reaction mixture has been consumed almost quantitatively byreaction.

Other reaction parameters are familiar to the person skilled in the artand can be chosen, for example, as described in EP-A-0 585 835, 0 496208, 0 69 866, in U.S. Pat. Nos. 5,124,427, 5,258,482 and 5,290,902 andalso DE-A-40 15 155 for the preparation of other biurets, allophanatesand isocyanurates.

The reaction of the compounds IV and V is usually carried out in thepresence of a catalyst in preferred quantities of from 10 to 5000 ppm byweight, based on the quantity of the compounds V employed.

Suitable catalysts are those which are generally known for thetrimerization reaction of isocyanate groups, ie. for example thequaternary ammonium hydroxides described in EP-A-0 649 866, eg.N,N,N-trimethyl-N-(2-hydroxypropyl)ammonium hydroxide, or the quaternaryammonium carboxylates known from EP-A-0 182 203, eg.N,N,N-trimethyl-N-(2-hydroxypropyl)ammonium 2-ethylhexanoate, ororganozinc compounds which are known as catalysts for allophanateformation, examples being zinc acetylacetonate or zinc 2-ethylcaproate.

The progress of the reaction is advantageously monitored by gelpermeation chroamtography (GPC) or by determining the NCO content of thereaction mixture.

The reaction is usually ended when almost all of the starting compoundIV has been converted, ie. can no longer be detected by GPC.

The reaction is conventionally ended by adding deactivators. Examples ofsuitable deactivators are inorganic or organic acids, the correspondinghalides, and alkylating agents. Specific examples are phosphoric acid,monochloroacetic acid, dodecylbenzenesulfonic acid, benzoyl chloride anddimethyl sulfate, and preferably dibutyl phosphate and di-2-ethylhexylphosphate. The deactivating agents can be employed in quantities of from1 to 200 mol %, preferably from 20 to 100 mol %, relative to thecatalyst.

After ending the reaction, any unreacted compound of the formula V isexpediently separated off from the reaction mixture, preferably down toa content of less than 1.0% by weight, particularly preferably less than0.5% by weight. If the compounds of the formula I are to be separatedfrom those of the formula III, this can be done by gel permeationchromatography. However, separation is unnecessary in the majority ofcases, since both compounds can be employed in two-componentpolyurethane coating compositions for similar purposes. The resultingproduct presents no handling problems and can generally be processedwithout special safety precautions.

The novel compounds of the formula I, alone or mixed with the compoundsII and III, are employed as the B component in two-componentpolyurethane coating compositions whose A component generally comprisesa hydroxy-functional polymer (A) devoid of isocyanate groups.

The hydroxy-functional polymers (A) are, for example, polymers with ahydroxyl content of from 0.1 to 20% by weight, preferably from 0.5 to10% by weight. The number-average molecular weight M_(n) of the polymersis preferably from 1000 to 100,000, particularly preferably from 2000 to10,000. Preferred polymers are those of whose weight more than 50% isaccounted for by C₁ -C₂₀ -alkyl (meth)acrylate, aromatic vinyl compoundshaving up to 20 carbon atoms, vinyl esters of carboxylic acids whichhave up to 20 carbon atoms, vinyl halides, nonaromatic hydrocarbonshaving 4 to 8 carbon atoms and 1 or 2 double bonds, unsaturatednitriles, and mixtures thereof. Particular preference is given topolymers consisting to the extent of more than 60% by weight of C₁ -C₁₀-alkyl (meth)acrylates or styrene, or mixtures thereof.

The polymers (A) additionally comprise hydroxy-functional monomers inaccordance with the above hydroxyl content and also, if desired, othermonomers, for example ethylenically unsaturated acids, especiallycarboxylic acids, acid anhydrides or acid amides.

Examples of other polymers (A) are polyesterols as obtainable bycondensing polycarboxylic acids, especially dicarboxylic acids, withpolyols, especially diols.

Other suitable polymers (A) are polyetherols prepared by adding ethyleneoxide, propylene oxide or butylene oxide onto H-active components.Polycondensation products of butanediol are also suitable.

The polymers (A) can of course be compounds with primary or secondaryamino groups.

Examples which may be mentioned are so-called Jeffamines, ie.amino-terminated polyetherols, or oxazolidines.

Apart from the abovementioned A and B components, the coatingcompositions can also comprise other polyisocyanates and compoundshaving polyisocyanate-reactive groups, such compounds customarily beingpresent in two-component coating compositions. Particularly suitableexamples of such compounds are the isocyanates used to prepare thecompounds of the formula I.

B components for two-component polyurethane coating compositionsgenerally contain

0.2-99.9 mol % of isocyanate groups in the form of the compound of theformula I

0.1-99.8 mol % of isocyanate groups in the form of a compound of theformula II and

0-58.2 mol % of isocyanate groups in the form of a compound of theformula III.

Preferred two-component polyurethane coating compositions comprise, as Acomponent,

a polymer (A) having at least 2 isocyanate-reactive groups, preferablyalcoholic hydroxyl groups,

the molar ratio of the sum formed from the units X, Y, U and V in thecompounds of the formulae I and III and the isocyanate-reactive groupsof polymer (A) to the sum of the isocyanate groups in the compounds ofthe formulae I, II and III being from 0.6:1 to 1.4:1, preferably from0.7:1 to 1.3:1.

Components B which are suitable for use in two-component polyurethanecoating compositions are obtained directly if the compounds IV arereacted with the compounds V in a molar ratio of from 1:50 to 1:1.5until almost all of the isocyanate-reactive groups R^(IV) have beenconsumed by reaction, and then the unreacted portion of the compounds Vis removed from the reaction mixture.

Mixtures which can be employed as one-component polyurethane coatingcompositions customarily contain

0.2-100 mol %, preferably 0.2-80 mol %, of isocyanate groups in the formof the compound of the formula I

0-58.2 mol %, preferably 10-49.9 mol %, of isocyanate groups in the formof a compound of the formula II and

0-58.2 mol %, preferably 10-49.9 mol %, of isocyanate groups in the formof a compound of the formula III.

It is advantageous to employ those coating compositions in which thereare

0.1-10 mol, preferably 0.2-5 mol, of a compound of the formula II permole of a compound of the formula I, and

0.6-1.4 mol, preferably 0.9-1.1 mol, of a compound of the formula IIIper mole of NCO groups in the compound of the formula II.

Preferred mixtures are those whose real content of isocyanate groups(NCO groups) is from 1 to 40% by weight, particularly preferably from 5to 25% by weight (taking the molecular weight of the NCO groups to be42) and with a theoretical NCO content of from -6 to +6% by weight,particularly preferably from -3 to +3% by weight.

The real NCO content in percent is obtained by measuring the molarquantity of NCO groups per unit weight, which can be found, for example,by generally known titration methods, and multiplying this value by 100and 42 (molecular weight of -NCO). A customary titration method isdescribed in DIN 53185.

The theoretical NCO content is obtained by calculation, by subtractingthe molar quantity of NCO groups per unit weight which corresponds tothe molar quantity of units X, Y, U and V per unit weight from themeasured molar quantity of the NCO groups per unit weight, andmultiplying the result by 4200.

The theoretical NCO content, in percent, is therefore the NCO contentwhich would have resulted had the protected, NCO-reactive groups (unitsX, Y, U and V) reacted quantitatively with the NCO groups, and for thecompounds I is equal to 0.

One-component systems of this kind have virtually unlimited storagelives and only crosslink in the presence of water, for example in theform of atmospheric moisture, since by means of the water the protectedunits X, Y, U and V are deprotected, ie. converted intoisocyanate-reactive groups. Through the choice of the stoichiometricratio, as defined, of the units X, Y, U and V to isocyanate groups itcan be made certain that the compounds form a high molecular weightnetwork, which is vital if the coatings are to attain a high level oftechnical performance.

The polyisocyanates II can also be replaced in whole or in part by othercompounds which react with the reactive component(s). Examples ofsuitable such compounds are polyepoxides, those containing acidanhydride groups or N-methylol groups, or those containing etherifiedN-methylol groups, examples being urea resins or melamine resins, whichare able to react with the deblocked groups X, Y, U and V of thecompounds I and III.

The novel coating compositions can additionally contain organicsolvents, for example xylene, butyl acetate, methyl isobutyl ketone,methoxypropyl acetate and N-methylpyrrolidone. Using solvents, the lowviscosity of the coating composition, as desired for processing, ie. forapplication to the substrates, is established. Owing to the compounds I,moreover, substantially less solvent is required; in other words, therelatively low viscosity desired is reached at higher solids contents.

The coating compositions can of course comprise other additives whichare customary in coating technology, for example pigments, fillers,leveling agents, etc.

They can also obtain catalysts for urethane formation, for exampledibutyltin dilaurate.

The two-component polyurethane coating compositions can be prepared in aknown manner. Commonly, the A component and the B component are mixedbefore the coating compositions are applied to a substrate. The desiredviscosity can be established by means of solvent.

The one-component polyurethane coating compositions can be prepared atany point in time prior to their application, since crosslinking isunable to take place spontaneously owing to the fact that theisocyanate-reactive amine, thiol and/or hydroxyl groups are present inprotected form, ie. as groups X, Y and, if appropriate, U and V.

Crosslinking takes place after application, when the coatingcompositions come into contact with water or atmospheric moisture.

Under the influence of water, the blocked, isocyanate-reactive groups inthe compounds I and III are liberated. Thereafter, the reaction of thedeblocked groups of the formulae I and III with the polyisocyanatestakes place at room temperature or at elevated temperature in a knownmanner.

Both the one- and two-component coating compositions can be applied tosubstrates in a customary manner, by spraying, flow coating, rolling,brushing, knife coating, etc.

The coating compositions are particularly suitable for workpieces withsurfaces of metal, plastic, wood, timber materials, etc.

The coatings obtained have very good mechanical properties, inparticular high hardness, flexibility and chemical resistance.

The novel compounds of the formula I have the particular advantage thatthey can be used to produce high-quality one- and two-componentpolyurethane coating compositions of particularly low viscosity.

The mixtures of compounds I and the mixtures of the compounds I, II andIII are also suitable for use as reactive diluents in two-componentpolyurethane systems, since they are able to participate in thecrosslinking reaction while having virtually no effect on thestoichiometric ratios of the NCO groups to the NCO-reactive groups.

EXAMPLES

Starting compounds of the formula IV

IV.1 2,2-Dimethyl-4-hydroxymethyl-1,3-dioxolane (isopropylideneglycerol)##STR34##

IV.2 4-Aminomethyl-2,2-dimethyl-1,3-dioxolane ##STR35## known from F. S.Gibson, M. S. Park and H. Rapoport, J. Org. Chem. 1994, 59, 7503-7507

IV.3 Reaction product of 3 mol of ethylene oxide and compound IV.1

To prepare IV.3, 1060 g (8 mol) of isopropylideneglycerol (IV.1) werecharged to a 5 l reactor suitable for preparing polyetherols, 4 g ofpotassium tert-butylate were added, and the mixture was heated to 110°C. At this temperature, 24 mol of ethylene oxide were added. Thereaction was continued until the pressure remained constant.

Reduced pressure was then applied for 30 minutes. After removal ofmonomer, the reactor was blanketed with nitrogen and cooled to 50° C.and the product was discharged. To remove the alkali, 3% by weight of aMg silicate (Ambusol, cation exchanger) was added and the mixture washeated at 100° C. for 2 h. The silicate was filtered off and the finalproduct was stabilized with 0.15% by weight of2,6-di-tert-butyl-p-cresol (Kerobit TBK).

OH number=216

V.4 2,2-Dimethyl-5-ethyl-5-hydroxymethyl-1,3-dioxane(Isopropylidene-TMP) ##STR36## To prepare IV.4, 250 g oftrimethylolpropane were refluxed with 750 ml of petroleum ether (boilingrange 30-75° C.), 750 ml of acetone and 0.15 g of p-toluenesulfonic acidmonohydrate for 24 h. The water of reaction produced was then removedusing a water separator. The solution was cooled, 0.5 g of sodiummethanolate was added, and the mixture was stirred at room temperaturefor 1 h. The solution was filtered, the solvent was removed on a rotaryevaporator and the residue was distilled under reduced pressure. Yield78% of theory, boiling point 71-72° C. (0.5 mbar).

IV.5 N-(2-Hydroxyethyl)-2-isopropyloxazolidine ##STR37## A. B Componentsfor Two-component Coating Compositions comprising compounds I

2000 g of hexamethylene diisocyanate (HDI) were charged to a reactorunder a nitrogen blanket, and the appropriate quantity of compound IV.1to IV.5, according to Table 1, was added. The mixture was heated to 80°C., 0.4 g of the catalyst DABCO TMR 1 (trade name of Air Products forN-(2-hydroxypropyl)trimethylammonium 2-ethylhexanoate) was added, thecomponents were reacted at this temperature and the reaction wasterminated, when the mixture had an NCO content of 39-41% by weight, byadding 0.4 g of di-2-ethylhexyl phosphate. In the case of product IV.2,the reaction mixture was heated at 120° C. without catalysis. Thereaction mixture was subsequently distilled in order to remove monomericHDI in a thin-film evaporator at an oil temperature of 165° C. under 2.5mbar. Subsequently, the content of residual HDI monomer in the endproduct was below 0.3% by weight.

Comparison Products, Prior Art

Product 1: BASONAT® HI 100, real NCO content=22.0%, viscosity at 25°C.=3900 mPas (polyisocyanate, BASF AG)

Product 2: BASONAT®P LR 8901, real NCO content=20.0%, viscosity at 25°C.=790 mPas (low viscosity polyisocyanate, BASF AG)

Novel Products

                  TABLE 1                                                         ______________________________________                                        B components                                                                           Starting             NCO    Viscosity                                         compound             content**                                                                            at 25° C.                         Product  IV       Molar ratio*                                                                              (% by wt.)                                                                           (mPas)                                   ______________________________________                                        3        IV.1     2.5         21.1   1590                                     4        IV.1     5.0         20.1   810                                      5        IV.1     10.0        18.4   680                                      6        IV.2     10.0        18.5   1310                                     7        IV.3     10.0        15.9   460                                      8        IV.4     2.5         20.9   2150                                     9        IV.4     5.0         19.6   2040                                     10       IV.4     10.0        17.7   2260                                     11       IV.5     2.5         20.5   1540                                     12       IV.5     5.0         19.1   1040                                     13       IV.5     10.0        17.0   1410                                     ______________________________________                                         *Proportion of starting compound of the formula IV relative to HDI [mol %     **real NCO content                                                       

Preparation and testing of two-component clearcoats of the novelpolyisocyanates

The novel products from Table 1 were mixed with a hydroxy-functionalvinyl polymer (LUMITOL® H 136, solids content=70%, OHN =136, BASF AG) inaccordance with the stoichiometric NCO:OH ratios, and the mixture wascatalyzed with 0.1% (based on the solids content) of dibutyltindilaurate (DBTL, Merck) in order to accelerate curing. Adjustment to anapplication viscosity of 20 s (DIN 53211 cup 4 mm flow-out nozzle) wasmade with butyl acetate. The solids contents of the coating materialwere determined in accordance with DIN V 53 216 part 1, while the VOCvalues were calculated from mass/volume ratios.

A film drawing frame was used to apply coatings with a wet filmthickness of 200 μm to glass plates. The resulting clearcoats were curedfor 7 days under standard climatic conditions. The properties of thecoatings obtained are summarized in Table 2. For comparison purposes,clearcoats containing BASONAT® HI 100 and BASONAT® P LR 8901 (BASF AG)were tested.

                                      TABLE 2                                     __________________________________________________________________________    Testing of clearcoats based on novel polyisocyanates against prior art        crosslinking agents                                                           Clearcoat of                                                                  product                                                                              (Compar. 1)                                                                         (Compar. 2)                                                                         4  5  7  9   10 13                                         __________________________________________________________________________    Solids content                                                                       45.6  50.9  53.6                                                                             58.7                                                                             61.0                                                                             53.1                                                                              64.5                                                                             52.7                                       [%]                                                                           VOC [g/l]                                                                            533   479   456                                                                              417                                                                              393                                                                              462 359                                                                              465                                        __________________________________________________________________________

The coating materials prepared using the novel polyisocyanatecrosslinking agents are not only of outstanding hardness (scratchresistance) and flexibility but also have an enhanced paint solidscontent relative to the prior art, or a lower solvent content(VOC=volatile organic compounds).

B. One-component polyurethane coating compositions and reactive diluentscomprising compounds I

Preparation of Products 14 to 17

6 mol of hexamethylene diisocyanate (HDI) were charged to a reactorunder a nitrogen blanket and 1.2 mol of the compound IV.1 to IV.5,according to Table 3, were added. The mixture was heated to 80° C., 150ppm by weight of the catalyst DABCO TMR 1 (trade name of Air Products,N-(2-hydroxypropyl)trimethylammonium 2-ethylhexanoate) were added, themixture was reacted at this temperature, and the reaction was stopped,at an NCO content of the mixture of 30-32% by weight, by adding 160 ppmby weight of di-2-ethylhexyl phosphate relative to HDI. The reactionmixture was subsequently distilled in order to remove monomeric HDI in athin-film evaporator at an oil temperature of 165° C. under 2.5 mbar.The content of residual HDI monomer in the end product after this wasless than 0.3% by weight.

Preparation of Products 18 to 20

6 mol of IPDI were charged to a reactor under a nitrogen blanket, and1.2 mol of the component IV were added. The mixture was heated to 70°C., 1200 ppm by weight (based on diisocyanate) of the catalyst DABCO TMR1 were added, the mixture was reacted at this temperature and thereaction was stopped, at an NCO content of the mixture of 25.5-26.5% byweight, by adding 1300 ppm by weight (based on diisocyanate) ofdi-2-ethylhexyl phosphate. The reaction mixture was subsequentlydistilled in order to remove monomeric IPDI in a thin-film evaporator atan oil temperature of 165° C. under 2.5 mbar.

Preparation of Products 21 and 22

6 mol of the diisocyanate were charged to a reactor under a nitrogenblanket, and 1.2 mol of isopropylideneglycerol (IV.1) were added. Themixture was heated to 80° C., 250 ppm by weight (based on diisocyanate)of the catalyst DABCO TMR 1 were added, the mixture was reacted at thistemperature, and the reaction was stopped, at an NCO content of themixture of 24% by weight in the case of BEPDI, or 26% by weight in thecase of IPCI, by adding 260 ppm by weight (based on diisocyanate) ofdi-2-ethylhexyl phosphate. The reaction mixture was subsequentlydistilled in order to remove monomeric diisocyanate in a thin-filmevaporator at an oil temperature of 165° C. under 2.5 mbar.

                  TABLE 3                                                         ______________________________________                                                        Starting NCO                                                  Product         compound theoretical                                                                           NCO real                                                                             Visc.                                 No.    Isocyanate                                                                             IV       [% by wt.]                                                                            [% by wt.]                                                                           [mPas]                                ______________________________________                                        14     HDI      IV.1     -1.7    16.2   490                                                                           (25° C.)                       15     HDI      IV.3     -0.3    13.8   510                                                                           (25° C.)                       16     HDI      IV.4     -1.3    15.2   2310                                                                          (25° C.)                       17     HDI      IV.5     -1.6    15.4   1220                                                                          (25° C.)                       18     IPDI     IV.1     -1.2    13.4   1470*                                                                         (50° C.)                       19     IPDI     IV.4     +0.1    13.7   2950*                                                                         (50° C.)                       20     IPDI     IV.5     -1.8    12.1   3040*                                                                         (50° C.)                       21     IPCI     IV.1     0.0     15.4   26240                                                                         (25° C.)                       22     BEPDI    IV.1     -1.8    12.0   19300                                                                         (25° C.)                       ______________________________________                                         * = 90% in butyl acetate                                                      HDI = Hexamethylene diisocyanate                                              IPDI = Isophorone diisocyanate                                                IPCI = 2Isocyanatopropylcyclohexyl isocyanate                                 BEPDI = 2Butyl-2-ethylpentamethylene diisocyanate                        

Preparation and Testing of One-component Coating Compositions

The novel products from Table 3 were mixed with Basonat® HI 100 (in thecase of negative theoretical NCO contents, in accordance with thestoichiometry), and 0.1% of dibutyltin dilaurate (DBTL, Merck) was addedin order to accelerate curing. Adjustment to an application viscosity of20 s (DIN 53 211 cup 4 mm flow nozzle) was made with butyl acetate. Thesolids contents of the coatings were determined in accordance with DIN V53 216 part 1, while the VOC values were calculated from mass/volumeratios.

The solids contents of paints are summarized in Table 4. For comparisonpurposes, a clearcoat based on Lumitol® H 136 (hydroxyacrylate resin,70% in butyl acetate, OHN=135, BASF AG), crosslinked with BASONAT® HI100 (polyisocyanate, 100%, real NCO content=22%, BASF AG) was tested.

                                      TABLE 4                                     __________________________________________________________________________    Clearcoat                                                                     from                                                                          isocyanate                                                                    No.   Comparison                                                                          14 15 16 17 18 20 21 22                                           __________________________________________________________________________    Solids                                                                              45.6  81.2                                                                             80.0                                                                             77.4                                                                             77.0                                                                             69.9                                                                             69.3                                                                             76.6                                                                             75.3                                         content [%]                                                                   VOC [g/1]                                                                           533   201                                                                              213                                                                              238                                                                              240                                                                              308                                                                              309                                                                              249                                                                              251                                          __________________________________________________________________________

The coating materials prepared with the novel isocyanate crosslinkingagents are not only of outstanding hardness (scratch resistance) butalso have a solids content which is markedly improved relative to theprior art, or a lower solvent content (VOC=volatile organic compounds).

Preparation and Testing of Mixtues as Reactive Diluents

Isocyanate No. 14 was mixed with the coating material of the comparisonexample from Table 4 in various proportions, and the mixture wascatalyzed with 0.1% of dibutyltin dilaurate (DBTL, Merck) in order toaccelerate curing. Adjustment to an application viscosity of 20 s (DIN53 211 cup 4 mm flow nozzle) was made with butyl acetate. The coatings'solids contents were determined in accordance with DIN V 53 216 part 1,while the VOC values were calculated from mass/volume ratios. Afilm-drawing frame was used to apply coatings with a wet film thicknessof 150 μm to glass plates. The resulting clearcoats were cured for 7days under standard climatic conditions. The resulting coatingsproperties are summarized in Table 5.

                  TABLE 5                                                         ______________________________________                                        Mixing ratio*                                                                 Isocynate No. 14                                                                            0        50     70    85   100                                  Standard coating material                                                                   100      50     30    15   0                                    Mixing ratio**                                                                Polyisocyanate No.1                                                                         0        56.4   75.1  88.0 100                                  Standard coating material                                                                   100      43.6   24.9  12.0 0                                    Erichsen indentation [mm]                                                                   8.9      9.9    10    10   10                                   Adhesion/cross-hatch                                                                        0.5      0      0     0    0                                    Scratch resistance                                                                          0        0      0     0    0                                    Solids content [%]                                                                          45.6     62.4   69.5  75.5 81.2                                 VOC [g/1]     533      382    316   259  201                                  ______________________________________                                         *the figure given is the weight ratio                                         **the figure given is the weight ratio relative to the respective solids      content of the components                                                

We claim:
 1. An isocyanato compound with capped, isocyanate-reactivegroups, of the formula I ##STR38## where R¹ and R² are hydrogen, C₁ -C₁₀-alkyl, C₆ -C₁₀ -aryl or C₇ -C₁₀ -aralkyl or together form C₃ -C₁₀-alkanediyl,X and Y are --O--, --S-- or ##STR39## where R⁴ is hydrogen,C₁ -C₂₀ -alkyl which is uninterrupted or interrupted by oxygen atoms inether function, or is C₆ -C₁₀ -aryl or C₇ -C₁₀ -aralkyl, R³ is C₁ -C₁₀-alkanediyl which together with --X--CR¹ R² --Y-- forms a 4-7-memberedring,in which either one hydrogen in R³ or the radical R⁴ in ##STR40##is replaced by an allophanate group R^(Ia) ##STR41## in which R⁵ is adivalent aliphatic, alicyclic, araliphatic or aromatic C₂ -C₂₀hydrocarbon unit,R⁶ is a single bond or a divalent aliphatic, alicyclic,araliphatic or aromatic C₁ -C₂₀ hydrocarbon unit or a mono- or poly(C₂-C₄ -alkylene oxide) unit, and R⁷ is a carbamoyl radical ##STR42## or abiuret group R^(Ib) ##STR43## in which one R⁸ is hydrogen and the otheris as defined for R⁷ or a biuret group R^(Ic) ##STR44## in which one R⁹is as defined for R⁷ and the other is as defined for R¹ or athioallophanate group R^(Id) ##STR45##
 2. A mixture comprising a)0.2-100 mol % of isocyanate groups in the form of the compound of thegeneral formula I according to claim 1b) 0-99.8 mol % of isocyanategroups in the form of a customary isocyanate having on average at least2 isocyanate groups (compound II) c) 0-58.2 mol % of isocyanate groupsin the form of a compound of the formula III ##STR46## where R¹ and R²are as defined for formula I,U and V are --O--, --S-- or ##STR47## whereR¹¹ is hydrogen, C₁ -C₁₀ -alkyl which is uninterrupted or interrupted byoxygen atoms in ether function, or is C₆ -C₁₀ -aryl or C₇ -C₁₀ -aralkyl,and R¹⁰ is C₁ -C₁₀ -alkanediyl which together with --U--CR¹ R² --V--forms a 4-7-membered ring, in which either one hydrogen of R¹⁰ or theradical R¹¹ in ##STR48## is substituted by a urethane group R^(IIIa)##STR49## or a urea group R^(IIIb) ##STR50## or a urea group R^(IIIc)##STR51## or a thiourethane group R^(IIId) ##STR52## in which R¹, R⁵ andR⁶ are as defined for formula I.
 3. A mixture as claimed in claim 2,where the compound II is of the general formula (IIa) ##STR53## or anoligomeric form deriving therefrom.
 4. A process for preparing a mixtureas claimed in claim 3, which comprises reacting a compound of theformula IV ##STR54## where R¹ and R² are as defined in formula I,##STR55## D and E are --O--, --S-- or ##STR56## where R¹³ is hydrogen,C₁ -C₁₀ -alkyl which is uninterrupted or interrupted by oxygen atoms inether function, or is C₆ -C₁₀ -aryl or C₇ -C₁₀ -aralkyl, andR¹² is C₁-C₁₀ -alkanediyl which together with D-CR¹ R² -E forms a 4-7-memberedring,in which either one hydrogen in R¹² or the radical R¹³ in ##STR57##is substituted by a radical R^(IVa)

    --R.sup.6 --OH,

a radical R^(IVb)

    --R.sup.6 --NH.sub.2,

or a radical R^(IVc) ##STR58## or a radical R^(IVd)

    --R.sup.6 --SH

with a compound of the formula V

    OCN--R.sup.5 --NCO

at from 20 to 140° C. with a molar ratio of the compound of formula IVto the compound of formula V of from 1:1.5 to 1:20.
 5. A process asclaimed in claim 4, wherein the unreacted portions of the compound ofthe formula V are separated off after the end of the reaction down to acontent of less than 1% by weight.
 6. A B component for two-componentpolyurethane coating compositions, comprising the mixture according toclaim 2, wherein0.2-99.9 mol % of isocyanate groups in the form of thecompound of the formula I
 0. 1-99.8 mol % of isocyanate groups in theform of a compound of compound II and0-58.2 mol % of isocyanate groupsin the form of a compound of the formula III.
 7. A two-componentpolyurethane coating composition comprisinga B component as claimed inclaim 6 and an A component having at least 2 NCO-reactive groupswith theproviso that the molar ratio of the sum formed from the units X, Y, Uand V in the compounds of the formulae I and III and the NCO-reactivegroups of the A component to the sum of the isocyanate groups in thecompounds of the formulae I, II and III is from 0.6:1 to 1.4:1.
 8. Aone-component polyurethane coating composition comprising the mixtureaccording to claim 2, wherein;0.2-100 mol % of isocyanate groups in theform of a compound of the formula I 0-58.2 mol % of isocyanate groups inthe form of a compound of compound II and 0-58.2 mol % of isocyanategroups in the form of a compound of the formula III.
 9. A coating methodwhich comprises coating an article with a two-component polyurethanecoating composition as claimed in claim
 6. 10. A coating method whichcomprises coating an article with a one-component polyurethane coatingcomposition as claimed in claim
 8. 11. A method of coating, comprisingcoating an article with a two-component polyurethane coating compositionas claimed in claim 7.